1. Field of the Invention
The present invention relates generally to a wireless charging device and method for using the same, and more particularly, to a resonance-type wireless charging device and method for performing charging through inductive coupling.
2. Description of the Related Art
In order to operate a mobile terminal, power must be continuously supplied. To provide continuous power, a mobile terminal is equipped with a battery, where the battery generally being charged by a charger. Research on contactless and wireless charging schemes have progressed in order to support portability in a charging scheme for charging a battery.
In particular, compared with a typical wireless charging scheme that uses inductive coupling over a short distance, a resonance-type wireless power transmission scheme capable of charging over longer distances has been recently proposed and researched.
Resonance-type wireless power transmission is based on evanescent wave coupling, in which an electronic wave moves from one medium to another medium over a short distance through an electronic field when the two media resonate in the same frequency. When a charging station connected to a power source forms such an electronic field and a wireless power reception device operating in the same resonance frequency as a MHz band of the electronic field approaches the charging station, an energy tunnel is created, thereby enabling charging of a portable device several meters away. Since the energy provided through resonance-type wireless power transmission is non-radiative and is based on a magnetic field, the energy is only delivered when a device having the resonance frequency exists. Thus, unlike other electronic waves, since non-used energy is reabsorbed into the electronic field instead of spreading to the air, the energy does not affect other surrounding machines or human bodies.
However, if a power reception resonator approaches a power transmission resonator, a mutual capacitance between the power reception and transmission resonators increases and a mutual inductance therebetween decreases, thereby changing a resonance frequency of the power reception and transmission resonators to a frequency different from a predefined frequency. If the resonance frequency of the power reception and transmission resonators moves, the efficiency of wireless power transmission decreases according to a decrease of a coupling coefficient due to frequency disharmony. In addition, output power of a power amplifier oscillated in a pre-fixed frequency decreases. Further, if a plurality of power reception resonators approaches the same power transmission resonator, the power reception resonators mutually act as parasitic components for each of the other plurality of power reception resonators, thereby decreasing a transmission/reception power gain and a Quality (Q)-factor.